Telecommunications Network Call Control

ABSTRACT

Telecommunications network components configured to manage call control of a communication session of user equipment are described herein. An anchoring network device may proxy signaling traffic for the communication session. The anchoring network device may determine a routing identifier based at least in part on which access network, or which type of access network, is carrying the communication session, and may transmit state information of the communication session to a call-control server in association with the routing identifier. The call-control server may provide control information of the communication session to the anchoring network device in response to the state information. The anchoring network device may modify the communication session, e.g., by adding or dropping one or more parties, in response to the control information. The routing identifier may be determined based at least in part on capabilities of a communication session indicated in a session-initiation message.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a nonprovisional application of, and claims priorityto and the benefit of, U.S. Patent Application Ser. No. 62/081,378,filed Nov. 18, 2014 and entitled “Distinct mscAddress in IDP on PerAccess Domain,” the entirety of which is incorporated herein byreference.

BACKGROUND

Modern telecommunications networks such as cellular telephone networkscan support a variety of advanced call-control services, such as callforwarding, pre-paid calling, adding or dropping call parties, orcommunicating pictures or video. For example, the CustomisedApplications for Mobile network Enhanced Logic (CAMEL) standard providescall-control services to users of second-generation (2G) andthird-generation (3G) cellular networks such as Global System for MobileCommunications (GSM) networks or Universal Mobile TelecommunicationsSystem (UMTS) networks. More recently, fourth-generation (4G) cellularnetworks such as Long Term Evolution (LTE) access networks,interoperating with Internet Protocol (IP) Multimedia Subsystem (IMS)core networks, have begun to provide packet-switched (PS) voice and dataconnections. Such packet-switched connections can provide greater speedand throughput than do circuit-switched (CS) connections, and can makepacket-switched data from other networks, such as the Internet, morereadily available. Most 4G cellular networks, however, stilladditionally use access networks that provide circuit-switchedconnections, such as GSM or UMTS, due to the substantial infrastructureinvestment needed to expand packet-switched access networks. Suchcircuit-switched access networks may provide comparable or, at times,better speed and quality than packet-switched access networks for sometypes of data, including synchronous communications such as full-duplexvoice communications.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items or features.

FIG. 1 illustrates an overview of devices involved in a call control ofa communication session of user equipment.

FIG. 2 illustrates an example telecommunications network, includingcomponents used to perform call control of the communication session.

FIG. 3 illustrates a component level view of user equipment capable ofengaging in a communication session.

FIG. 4 illustrates a component level view of a telecommunicationsnetwork device capable of managing call control of a communicationsession of user equipment, e.g., to provide advanced services.

FIG. 5 is a call flow showing an example of call control with respect toan originating mobile terminal.

FIG. 6 is a call flow showing an example of call control with respect toa terminating mobile terminal.

FIG. 7 illustrates an example process performed by an anchoring networkdevice of a telecommunications network for enabling call control of acommunication session.

FIG. 8 illustrates an example process performed by an anchoring networkdevice of a telecommunications network for carrying out call control ofa communication session.

DETAILED DESCRIPTION Overview

This disclosure describes, in part, a telecommunications networkconfigured to implement call control of a communication session of userequipment. Throughout this disclosure, the noun “call” is synonymouswith “communication session” unless otherwise specified. The userequipment may be a cellular telephone, such as a feature phone orsmartphone. The communication session may be anchored at an anchoringnetwork device. The anchoring network device may determine a routingidentifier based at least in part on capabilities of the communicationsession such as an access-network type, transmit the routing identifierand state information of the communication session to a call-controlserver, receive control information, and modify the communicationsession according to the control information. For example, the anchoringnetwork device may add, drop, or transfer participants in thecommunication session as specified by the control information. Thecapabilities of a communication session are determined in part on, e.g.,the user equipment and access networks involved. Providing a routingidentifier can permit the call-control server to provide servicesappropriate to the particular devices involved in a particularcommunication session.

In some examples, call control is performed on or in new or existingcommunication sessions. Example call-control functions can be providedby IMS application servers (ASes) such as a telephony application server(TAS) or a service centralization and continuity application server(SCC-AS), CAMEL servers, or Signaling System 7 (SS7) Intelligent NetworkApplication Protocol (INAP) servers. Example call-control functions caninclude, but are not limited to, adding, dropping, or transferringparticipants to, from, or between communication sessions; multi-partyconferencing; transmitting multimedia data (e.g., video calling orvideoconferencing); injecting voice announcements, intercept tones, orother audio or media into a communication session; number redirection,e.g., for toll-free calls, “N-1-1” or other calls not tied to a specificarea code (e.g., in the United States, 9-1-1 for emergencies or 5-1-1for traffic information), hunt groups, backup phone numbers, short-digitextension dialing, or user-specified call forwarding; calling-card orprepaid calling; adjusting rate or charging information of thecommunication session; processing of vertical service codes or othercodes for, e.g., repeat dialing, call return, intercom ringing, callblocking, anonymous calling, do not disturb, or other custom local-areasignaling services; voicemail, time-and-date, or other interactive voiceresponse (IVR) services; voice or face recognition based on mediatransmitted during a communication session; or collecting dual-tonemulti-frequency (DTMF) tones.

FIG. 1 illustrates an example telecommunications network 100 and showsan overview of devices involved in provision of call-control services touser equipment. The telecommunications network 100 includes userequipment (UE) 102(1)-102(N) (individually or collectively referred toherein with reference 102), where N is any integer greater than or equalto 1. The UE 102 (a “terminal”) may be or include any sort of devicecapable of cellular or wireless network communication, such as acellular phone, a tablet computer, a personal digital assistant (PDA), apersonal computer (PC), a laptop computer, a media center, a workstation, etc. Examples of UE 102 are described below with reference toFIG. 3.

In some embodiments, the UE 102 may have a radio and be configured totune that radio to licensed wireless spectrum utilized bypacket-switched access networks, such as LTE access networks. UE 102 mayalso be configured to tune the radio to wireless spectrum utilized bycircuit-switched access networks, such as GSM access networks or UMTSaccess networks. UE 102 may also be configured to tune the radio towireless spectrum utilized by local-area network (LAN) (or personal-areanetwork, PAN, and likewise throughout) access networks, such as WIFInetworks. When equipped with a single radio, UE 102 may only beconnected to one of these access networks at a time.

In some examples, UE 102 can communicate, e.g., via a first accessnetwork 104 of a first type or a second access network 106 of a second,different type. The first type may be a packet-switched (PS) type (e.g.,LTE) and the second type may be a circuit-switched (CS) type (e.g.,GSM). UE 102 may participate in a handover between first access network104 and second access network 106, e.g., as a user moves in and out ofcoverage areas of individual access networks 104 or 106.

In some examples, the first access network 104 or the second accessnetwork 106 may be any sort of access network, such as a GSM or UMTSnetwork; a universal terrestrial radio network (UTRAN) or an EnhancedData rates for GSM Evolution (EDGE) radio access network (GERAN); anevolved universal terrestrial radio access network (E-UTRAN), a WIFI(IEEE 802.11) or other LAN access network; or a satellite or terrestrialwide-area access network such as a wireless microwave access (WIMAX)network. In some examples, the first access network 104 or the secondaccess network 106 may include a base station (a “NodeB”), as well as aradio network controller (RNC). In some examples, the first accessnetwork 104 or the second access network 106 may use any sort of airinterface, such as a code division multiple access (CDMA), time divisionmultiple access (TDMA), or frequency division multiple access (FDMA) airinterface. In some examples, the first access network 104 may providedpacket-switched connections and the second access network 106 mayprovide circuit-switched connections. In some examples, the first accessnetwork 104 may be a packet-switched cellular type of access network andthe second access network 106 may be a packet-switchedlocal-area-network type of access network. Examples of LAN accessnetworks can include IEEE 802.11 (WIFI) and IEEE 802.15.1 (BLUETOOTH).

In some examples, wired access networks may be used, exclusively or incombination with wireless access networks. Examples include Plain OldTelephone Service, POTS, or Public Switched Telephone Network, PSTN,lines, optical (e.g., Synchronous Optical NETwork, SONET) technologies,Asynchronous Transfer Mode (ATM), and other network technologies, e.g.,configured to transport Internet Protocol (IP) packets. In someexamples, the telecommunications network 100 can include or becommunicatively connected with an interworking function (IWF) or otherdevice bridging networks, e.g., LTE, 3G, and POTS networks. In someexamples, the IWF can bridge Signaling System 7 (SS7) traffic from thePSTN into the telecommunications network 100, e.g., permitting PSTNcustomers to place calls to cellular customers and vice versa.

In the illustrated example, UE 102 can communicate via first accessnetwork 104 with a telecommunications network device 108 (e.g., mobilitymanagement entity, MME), or via second access network 106 with a server110. In some embodiments, the server 110 may be or include a mobileswitching center (MSC) server (MSS) associated with the second accessnetwork 106, e.g., a CS access network. The telecommunications networkdevice 108 and the server 110 are examples of access devices that cancontrol or modify communications with UE 102 via access network(s) 104or 106.

A handover between access networks can include, for example, a handoverfrom packet-switched first access network 104 to circuit-switched secondaccess network 106. However, handover is not limited to that example. Ahandover in various examples can be a handover from a circuit-switchedaccess network to a packet-switched access network, or in generalbetween a first access network of a first type and a second accessnetwork, e.g., of the first type or of a second, different type. Examplenetwork types may include WI-FI networks carryingvoice-over-Internet-Protocol (VoIP) communication sessions, wirelinenetworks such as Ethernet, or wireless networks such as those used forcommunications via satellites.

The user equipment 102 may further be configured to initiate or receivea communication session, such as a voice call, a video call, or anothersort of synchronous communication. Initiation of such communications mayinvolve communication clients and session initiation protocol (SIP)clients communicatively connected with components of thetelecommunications network, e.g., call-control components 112.Initiation and call control of a communication session, and componentsinvolved therein, are illustrated in FIGS. 2, 3, and 4 and described infurther detail herein.

The UE 102 may initiate the communication session using a connection tothe first access network 104. The first access network 104 may besecured using, for example, information from a Subscriber IdentityModule (SIM) card of the UE 102, or may be non-secured. The first accessnetwork 104 connects the UE 102 to a telecommunications network. Arouting device of the first access network 104 may communicate with adevice of the telecommunications network 100, such as thetelecommunications network device 108.

The telecommunications network device 108 may include a gateway device,such as an Evolved Packet Data Gateway (ePDG). An exampletelecommunications network device 108 is illustrated in FIG. 4 anddescribed below with reference to that figure. Further, thetelecommunications network device 108, as well as the server 110 and thecall-control components 112, may each be or include a server or serverfarm, multiple, distributed server farms, a mainframe, a work station, apersonal computer (PC), a laptop computer, a tablet computer, anembedded system, or any other sort of device or devices. In oneimplementation, one or more of telecommunications network device 108,the server 110, and the call-control components 112 may represent aplurality of computing devices working in communication, such as a cloudcomputing network of nodes. Also, the telecommunications network device108, the server 110, and the call-control components 112 may each be orinclude devices of a telecommunications network. In various embodiments,the call-control components 112 represent components of an IMS of thetelecommunications network. Examples of such components are describedbelow with reference to FIG. 2. Examples of the telecommunicationsnetwork device 108, the server 110, and the call-control components 112are illustrated in FIG. 2 and are described in greater detail withreference to that figure.

As noted above, the Session Initiation Protocol (SIP, RFC 3261) can beused to establish and manage communication sessions. A communicationsession typically passes through several phases over its life. These aredescribed with reference to a voice call in the circuit-switched domainbut are not limited thereto. For LTE, the phases are defined in 3GPP TS24.237 version 12.6.0 Release 12, p. 19 and in 3GPP TS 24.229 version10.9.0 Release 10, pp. 96-98, or subsequent versions of those standards.

To initiate a communication session, e.g., in response to a user'sdialing a phone number (e.g., “867-5309”), originating user equipment102(1) sends a SIP INVITE request via first access network 104 toterminating user equipment 102(N). This begins a “pre-alerting” phase ofthe session in some examples. In some examples, pre-alerting begins whenthe terminating user equipment 102(N) responds with a SIP 100 Trying, aSIP 183 Session in Progress, or both. The terminating user equipment102(N) then provides a SIP response carrying a 180 response code,signifying “Ringing.” This begins an “alerting” phase of the session,during which the terminating user equipment 102(N) provides anindication, e.g., to a user thereof, that a call is incoming Examples ofindications include vibrations and audible ringtones. The SIP responseis referred to as a “SIP 180 Ringing response”, and likewise for otherSIP response codes described herein. As used herein, a SIP response codeending in “xx”, e.g., a SIP 1xx Provisional response, signifies anyresponse of, e.g., class 1 of SIP responses (RFC 3261, §7.2).

When terminating user equipment 102(N) accepts the communication session(e.g., a user of UE 102(N) chooses to answer the call), terminating userequipment 102(N) sends a SIP 200 OK response to originating userequipment 102(1). This begins an “established” phase of thecommunication session, during which data can be exchanged betweenoriginating user equipment 102(1) and terminating user equipment 102(N).In an example, the data includes digitized audio of a voice call. Thealerting and pre-alerting phases are referred to collectively as a“pre-establishment phase.” The pre-establishment phase corresponds to aSIP “early dialog state” and the established phase corresponds to a SIP“confirmed dialog state” (RFC 3261, §12).

In some examples, SIP requests and responses may pass to or throughvarious SIP proxies, user-agent servers or clients, or back-to-back useragents (B2BUAs). As used herein, an “anchoring network device” is a corenetwork device (e.g., integrated with telecommunications network device108, server 110, call-control component 112, or another component suchas a TAS or SCC-AS) through which SIP traffic for a communicationsession is proxied (or otherwise passes, and likewise throughout) forthe duration of the established phase. That session is “anchored” at theanchoring network device. Anchoring SIP traffic for a session canincrease network robustness by isolating the two sides of the anchoringnetwork device. For example, terminating user equipment 102(N) is notrequired to change its SIP route to originating user equipment 102(1)when originating user equipment 102(1) is handed over from first accessnetwork 104 to second access network 106, since that SIP route passesthrough an anchoring network device. In some examples, anchoring takesplace in response to receipt by an anchoring network device of a SIPINVITE, and the anchoring network device transmits a SIP 183 Session inProgress once anchoring is complete, i.e., once anchoring network devicehas recorded an indication that the communication session is anchored atthat anchoring network device. In some examples, the anchoring networkdevice includes at least a TAS or a service switching function (SSF)such as a CAMEL gsmSSF or IMS SSF (IM-SSF).

Call-control services are generally provided by call-control components112 independently of the type of access network(s) used for anyparticular communication session. This permits providing consistentcall-control services between, e.g., PS and CS callers, or throughout acommunication session when one party leaves a PS coverage area and handsover to a CS access network. However, in some prior schemes, thisindependence can prevent effectively providing differentiated servicesspecific to particular types of access networks. For example, it may bedesirable to provide video-calling services only to terminals connectedvia high-speed access networks such as an LTE network. In anotherexample, it may be desirable to charge call minutes against a pre-paidaccount when UE 102 is connected via a cellular access network, but notwhen UE 102 is connected via a LAN access network. It is thereforedesirable to provide the call-control components 112 informationregarding the access network(s) used in a communication session or otherinformation regarding capabilities of the communication session. Someprior schemes do not provide this information.

Throughout this disclosure, other devices can be used in conjunctionwith listed devices. For example, a telecommunications network caninclude many core network devices, only some of which implementfunctions described herein for core network devices. Similarly, atelecommunications network can include many anchoring network devices,only some of which implement functions described herein for anchoringnetwork devices.

Example Telecommunications Network

FIG. 2 illustrates an example telecommunications network 200. Userequipment 202 communicates with access system 204 of thetelecommunications network. Access system 204 can include a first accessnetwork of a first type (e.g., LTE) and a second access network of asecond, different type (e.g., WIFI). Each of the first access networkand the second access network can be configured to selectively carry acommunication session of user equipment 202. For example, voice callscan be carried over the first access network using voice-over-LTE(VoLTE) and over the second access network using voice-over-WIFI(VoWIFI). In some examples, the first type is a packet-switched cellulartype and the second type is a packet-switched local-area-network type.IMS 206 communicates with access system 204 and provides media-handlingservices, e.g., to route video or voice data or to maintain continuityof the communication session during handover of the communicationsession.

In the illustrated example, access system 204 includes at least an MME208 associated with a packet-switched access network 210, a bridge 212(or other packet relay) associated with a LAN-based access network 214,or an MSS 216 associated with a circuit-switched access network 218. Inan example, the packet-switched access network 210 is the first accessnetwork and the LAN-based access network 214 is the second accessnetwork.

The packet-switched access network 210, e.g., an LTE access network, mayinclude an eNodeB 220, e.g., a 4G base station or other access point,that provides connectivity to the packet-switched access network 210.The LAN-based access network 214, e.g., a WIFI network, may include awireless access point (WAP) 222, e.g., a WIFI WAP, that providesconnectivity to the LAN-based access network 214. The circuit-switchedaccess network 218 may include a CS base station 224 that providesconnectivity to the circuit-switched access 218. The IMS 206 of thetelecommunications network may include a number of nodes, such as aproxy call session control function (P-CSCF) 226, a home locationregister (HLR)/home subscriber server (HSS) 228, an interrogating callsession control function (I-CSCF) 230, a serving call session controlfunction (S-CSCF) 232, an a TAS 234, and a call-control server 236. Thecall-control server 236 can alternatively be located outside the IMS 206and be communicatively connected with the IMS 206. The call-controlserver 236 can include, e.g., a service control point (SCP) aimplementing a service control function (SCF) such as a gsmSCF, or anintelligent peripheral implementing a specialized resource function(SRF). In some examples, the call-control server 236 can include a CAMELserver. In some examples, the call-control server 236 can be included inor integrated with a CAMEL server or other intelligent-network server.

The telecommunications network may also include a number of devices ornodes not illustrated in FIG. 2. Such devices or nodes may include anaccess transfer control function (ATCF), an access transfer gateway(ATGW), a visitor location register (VLR), a serving general packetradio service (GPRS) support node (SGSN), a gateway GPRS support node(GGSN), a policy control rules function (PCRF) node, a serving gateway(S-GW), a session border controller (SBC), or a media gateway. IMS 206may further include a number of devices or nodes not illustrated in FIG.2, such as a presence server and one or more additional CSCFs. A corenetwork of the telecommunications network may be a GPRS core network oran evolved packet core (EPC) network, or may include elements from bothtypes of core networks.

The telecommunications network may provide a variety of services to userequipment 202, such as synchronous communication routing across a publicswitched telephone network (PSTN). Further services may include callcontrol, switching, authentication, billing, etc. In at least oneexample, IMS 206 functions and devices communicate using specificservices provided by the access system 204 or elements thereof, but arenot directly tied to those specific services. For example, IMS 206devices can intercommunicate using an EPC network, a GSM network, aSONET network, or an Ethernet network.

In initializing a communication session, the user equipment 202 mayregister the communication session with the IMS 206 of thetelecommunications network. To do this, the user equipment 202 sends aninitiation SIP REGISTER request to the IMS 206 via an access network,e.g., via the eNodeB 220 and MME 208 of the packet-switched accessnetwork 210. The P-CSCF 226 of the IMS 206 may receive the SIP REGISTERrequest. P-CSCF 226 may forward the REGISTER request directly to S-CSCF232, or may forward the request to I-CSCF 230, which can locate anappropriate S-CSCF 232, e.g., using stored database information, andforward the REGISTER request to the located S-CSCF 232. In someexamples, the P-CSCF 226 is located in a visited network of UE 202 andthe I-CSCF 230 and S-CSCF 232 are located in a home network of UE 202.The S-CSCF 232 or other components (omitted for brevity) of the IMS 206can store information about the user equipment 202 in the HLR/HSS 228and then send a SIP response to the user equipment 202 to complete theIMS registration of the communication session.

In an example of call-control services, a signaling path (“SIG”) of thecommunication session passes through P-CSCF 226, S-CSCF 232, and TAS234, as indicated by the dash-dot arrow. After TAS 234, the example SIPsignaling path passes back through S-CSCF 232 to a peer (not shown). Inan example in which UE 202 is an originating (MO) UE, the peer can be,e.g., an S-CSCF corresponding to a terminating (MT) UE (omitted forbrevity). As shown, in this example, the signaling path does not reachthe call-control server 112. In the illustrated example, the TAS 234 isan anchoring network device and proxies signaling traffic for thecommunication session, e.g., operating as a SIP proxy or B2BUA. Inanother example, the MSS 216 can be the anchoring network device and canproxy signaling traffic for the communication session, e.g., GSM or SS7signaling traffic. In some examples, the anchoring network device caninclude an IP-Short Message (SM) Gateway AS or a Rich CommunicationsServices (RCS) AS. In some examples, the anchoring network device can beincluded in or integrated with a TAS or other core network device.

The TAS 234 (or other anchoring device, and likewise throughout) cancommunicate with a call-control server 236 to provide call-controlservices to UE 202. In some examples, the TAS 234 includes an SSF, suchas a gsmSSF or IM-SSF, configured to communicate with call-controlserver 236, e.g., via the CAMEL or INAP protocols. In some examples, inresponse to a particular ongoing state or a particular change in stateof the communication session, the TAS 234 can transmit state informationincluding an indication of the state to the call-control server 236. Forexample, the TAS 234 can notify the call-control server 236 when acommunication session is established or terminated, when alerting beginsat the called party, when the called party answers, does not answer, oris busy, when DTMF tones are detected during a communication session, orwhen a handover is to occur or has occurred. In some examples, the TAS234 can be configured to determine a routing identifier as describedbelow and to transmit the state information of the communication sessionto the call-control server 236 in association with the routingidentifier.

In response to the notification from the TAS 234, e.g., the stateinformation of the communication session, the call-control server 236can determine control information of the communication session. Thecall-control server 236 can determine the control information based atleast in part on the routing identifier, as discussed below. Thecall-control server 236 can then transmit or otherwise provide thecontrol information to the TAS 234. The TAS 234 can modify the state ofthe communication session based at least in part on the controlinformation. For example, the TAS 234 can add or drop one or moreparties to the communication session, or perform other call-controlfunctions such as those described above, in response to the controlinformation from the call-control server 236.

In some examples, the TAS 234 is configured to determine a routingidentifier based at least in part on information of the one of the firstaccess network and the second access network carrying the communicationsession. An example of such information includes information of which ofthe first access network and the second access network is carrying thecommunication session, e.g., an identifier of an access network of thecommunication session such as a cell identifier or WAP media accesscontrol (MAC) address. In some examples, the TAS 234 is configured todetermine a routing identifier based at least in part on a type of theaccess network carrying the communication session. In some examplesusing access networks of different types, there can be a uniqueaccess-network type for each access network, and the TAS 234 candetermine the routing identifier based at least in part on which accessnetwork or based at least in part on the access-network type; in theseexamples, those two determinations are equivalent. In some examples, theTAS 234 is configured to determine a routing identifier based at leastin part on information identifying the user equipment 102, such as aninternational mobile subscriber identity (IMSI), information identifyingthe communication session, such as a correlation mobile stationinternational subscriber directory number (C-MSISDN), or an identifierof one or more core network components, such as a session transfernumber-single radio (STN-SR).

In some examples, the routing identifier includes an E.164 or othertelephone number. In some examples, the routing identifier includes alocation number or location-number prefix. In some examples, the routingidentifier includes an identifier formatted as a location or address ina protocol used for communication between the TAS 228 and thecall-control server 236. For example, in a configuration using the CAMELApplication Part (CAP) protocol, the TAS 234 can provide the stateinformation to the call-control server 236 in an Initial Detection Point(Initial DP or IDP) message, e.g., as defined in 3GPP TS 23.078 V12.0.0(2014-10), §4.6.1.8. The IDP message can include at least locationinformation indicating an address, e.g., an E.164international-dialing-plan telephone number, of UE 202, or an MSCaddress indicating an address of the anchoring network device (e.g., MSS216 or TAS 234). The TAS 234 can determine the routing identifier bymodifying or replacing existing address information in the IDP record.Examples of CAP IDP fields are discussed herein; other IDP fields, orfields of records defined in other protocols, can additionally oralternatively be modified or replaced to carry routing identifiers.

In some examples, the TAS 234 can determine an access-network type ofthe communication session based at least in part on the signalingtraffic, e.g., a SIP P-Access-Network-Info header included with, e.g., aSIP REGISTER request or a SIP INVITE request from the UE 202. In someexamples, the TAS 234 can determine the routing identifier using astored mapping of access-network types to corresponding routingidentifiers. Examples are shown in Table 1. The TAS 234 can include therouting identifier in the “mscAddress” field of the CAP IDP message insome examples. Routing identifiers such as those listed in the rightcolumn of Table 1 can be selected, e.g., from address ranges allocatedfor network use and thus not in use by terminals.

TABLE 1 Access-Network Type Routing Identifier (E.164), e.g., CAPmscAddress IEEE 802.11 11111111111 3GPP E-UTRAN 22222222222 3GPP UTRAN33333333333 3GPP GERAN 44444444444

In other examples, the TAS 234 can determine a location prefix using astored mapping of access-network types to location prefixes, and formthe routing identifier including the location prefix followed by anaddress of the UE 202, e.g., indicated in a SIP To or From header.Example prefixes are shown in Table 2.

TABLE 2 Access-Network Type Routing Identifier, e.g., location prefixIEEE 802.11 11 3GPP E-UTRAN 22 3GPP UTRAN 33 3GPP GERAN 44

E.164 addresses such as those carried in the “mscAddress” or “LocationNumber” fields of a CAP IDP request, or the “Location Number” subfieldof the “Location Information” field of a CAP IDP request, can include upto 15 digits, including the country code. Most phone numbers currentlyin use have fewer than 15 digits, permitting space for a prefix. Forexample, the German number +49 33203 877 2021 has 14 digits (the “+” isnot part of the number), permitting a 1-digit prefix, and the US number+1 800 866 2453 has 11 digits, permitting a 4-digit prefix. For example,for an MO call from +61 491 570 110 via a 3GPP UTRAN (3G GSM), therouting identifier can be an mscAddress of “33333333333” (as in Table1), or a Location Number of “3361491570110” (as in Table 2). For such acall via a 3GPP E-UTRAN (LTE), the routing identifier can be anmscAddress of “22222222222” (as in Table 1), or a Location Number of“2261491570110” (as in Table 2).

In some examples, an IP-SM gateway can include the routing identifier inan “smscAddress” field of an IDP message. In some examples, an RCS AScan include the routing identifier in the mscAddress field. In someexamples, multiple routing identifiers can be used, e.g., as at leasttwo of an mscAddress, smscAddress, and a prefix to the Location Number.In some examples, the TAS 234 can transmit, in association with arouting number, e.g., of any of the types or in any of the fieldsdescribed above, an address of user equipment participating in thecommunication session. For example, the TAS 234 can transmit theLocation Number of “2261491570110” including the E.164 address“61491570110” in association with the location prefix “22”.

In some examples, the TAS 234 can be responsive to a control message toenable or disable the generation of routing identifiers, e.g., withrespect to some or all communication sessions anchored by the TAS 234.In some examples, the TAS 234 can store the routing identifier(s) incall detail record(s) (CDRs) corresponding to the communication session.In some examples, the TAS 234 can provide routing identifiers or otherinformation to the call-control server 236 based at least in part onuser information retrieved from the HLR/HSS 228, e.g., CAMEL servicekeys (SKs). For example, the TAS 234 can provide routing identifiersonly for users associated with specific SKs.

In some examples, the TAS 234 can include a memory, e.g., acomputer-readable memory, storing a mapping between access-network typesand routing identifiers. The TAS 234 can be configured to receive amodification instruction and modify the mapping in response to themodification instruction. This can permit dynamically updating therouting identifiers or assignments of routing identifiers tocapabilities, increasing flexibility of the telecommunications network.

The call-control server 236 can extract the routing identifier from,e.g., the mscAddress or Location Number fields. The call-control server236 can then determine the control information, e.g., based at least inpart on the routing identifier (e.g., “33333333333” or “33” in the UTRANexamples above). The call-control server 236 can additionally determinethe control information, e.g., based at least in part on informationabout one or more parties to the communication session. The call-controlserver 236 can retrieve this information, e.g., from the HLR/HSS 228.

In some examples, the telecommunications network 200 includes a routingnetwork device (“router”) 238 configured to communicatively connect theTAS 234 and the call-control server 236. In some examples, the router238 can be or include an SS7 signaling transfer point (STP). In someexamples, the call-control server 236 is configured to transmit therouting identifier (from TAS 234) in association with the controlinformation. The router 238 is configured to determine a network addressof the TAS 234 (or other anchoring network device, as noted above) basedat least in part on the routing identifier transmitted in associationwith the control information. For example, the router 238 can store amapping from routing identifiers to network addresses. The router 238 isconfigured to convey the control information to the TAS 234 using thedetermined network address. In an example, the TAS 234 provides therouting identifier as an mscAddress. This address is the address thecall-control server 236 expects to use to provide the controlinformation to the TAS 234 in this example. The router 238 can map fromthe routing identifier (e.g., “33333333333”) to a network address of theTAS 234, e.g., an E.164 identifier such as +1 800 555 0199, an IP orIPv6 address, or an SS7 point code. The router 238 can determine thenetwork address based at least in part on the routing identifier orother information transmitted in association with the controlinformation, e.g., any fields of the reply to a CAMEL IDP message. Usingrouter 238 can permit call-control server 236 to interoperate withmultiple anchoring network devices without requiring call-control server236 to store network addresses of all the anchoring network devices,reducing memory requirements and processing load on the call-controlserver 236.

For clarity, the illustrated example is in the context of determining arouting identifier based at least in part on access-network type.However, corresponding components and functions described above can beused for determination or processing of routing information based atleast in part on capabilities of the communication session in additionto or instead of access-network type. In these and other examples, theTAS 234 (or other anchoring network device, as noted above) candetermine the routing identifier based at least in part on informationin addition to or instead of information about the access network for acommunication session.

In some examples, the TAS 234 can receive a session-initiation message,e.g., a SIP INVITE request or SIP 1xx response (e.g., a SIP 183response), indicating capabilities of a communication session. The TAS234 can determine a routing identifier of the anchoring network devicebased at least in part on the capabilities. Techniques discussed abovewith reference to the determination of routing identifiers based atleast in part on access-network type can be used in determining routingidentifiers based on capabilities. For example, the anchoring networkdevice can store a table mapping capability values or combinations ofcapability values to routing identifiers. The TAS 234 can transmit therouting identifier and state information of the communication session toa call-control server 236, as discussed above.

The capabilities can be indicated, e.g., in a header or body of the SIPrequest or response, such as a Session Description Protocol (SDP) body.The capabilities can include at least an access-network type of thecommunication session, a device type of user equipment 202 participatingin the communication session, location information of the user equipment202, a media capability of the user equipment 202 (e.g., whether or notthe UE 202 supports video, or which codecs the UE 202 supports), avirtual-network identifier of the user equipment (e.g., identificationof a mobile virtual network operator, MVNO, of UE 202), or anauthentication type of the user equipment (e.g., SIM-based or other).

As discussed above, the TAS 234 can receive, from the call-controlserver 236, control information. The TAS 234 can modify thecommunication session based at least in part on the control information,e.g., as discussed above.

In some examples, such as for IMS-capable users registering via a CSaccess network 218, the anchoring network device can receive anindication of user equipment 202, e.g., from MSS 216. The anchoringnetwork device can transmit a request for registration informationcorresponding to the user equipment. The request can be transmitted,e.g., to HLR/HSS 228. The anchoring network device can, in response tothe transmitted request, receive the session-initiation message, e.g., aDiameter message, indicating capabilities of communication sessions inwhich UE 202 may participate. This can permit providingcapability-specific call-control services even to terminals that are nottransmitting SIP signaling.

The devices and networks illustrated in FIG. 2 may be examples of thedevices and networks illustrated in FIG. 1 and described above. Forinstance, the MME 208 may be a telecommunications network device 108,the user equipment 202 may be user equipment 102, the IMS 206 and itscomponents 226, 228, 230, 232, 234, or 236 may include one or morecall-control components 112, and the MSS 216 may be a server 110. Also,the eNodeB 220 may be an access point for the packet-switched accessnetwork 210, and the CS base station 224 may be a base station for thecircuit-switched access network 218. Accordingly, the descriptions ofthe devices and networks of FIG. 1 apply to the devices and networks ofFIG. 2. The devices and networks of FIG. 2 may cooperate to accomplishcall control, e.g., as shown in FIG. 1 and described above. They mayalso cooperate to accomplish the initialization of a communicationsession of user equipment 202.

Example Devices

FIG. 3 illustrates a component level view of user equipment 300 capableof at least some of connecting to a plurality of access networks,engaging in a communication session, originating or receiving signalingtraffic, reporting capabilities of a communication session, or handingover (switching access networks) during the communication session. Userequipment 300 may be any sort of user equipment, such as user equipment102 or 202. As illustrated, user equipment 300 comprises a system memory302 storing communication client(s) 304, capability module 306, SIPclient 308, and radio resource control 310. Also, example user equipment300 includes processor(s) 312, a removable storage 314, a non-removablestorage 316, radio 318, a display 320, output device(s) 322, inputdevice(s) 324, and one or more antenna(s) 326 connected to radio 318.Processor 312, radio 318, system memory 302, and other illustratedcomponents of user equipment 300 can be communicatively coupled via bus328, e.g., a PCI or other computer bus. In some examples, a single-radiovoice call continuity (SRVCC) module, omitted for brevity, can performfunctions including receiving instructions, such as instructionspreparing user equipment 300 for a handover or instructions to completea handover by tuning the radio 318, performing measurements of accessnetworks, generating measurement reports that include the measurements,and providing the measurement reports to the telecommunications network.

In various embodiments, system memory 302 is volatile (such as RAM),non-volatile (such as ROM, flash memory, etc.), or some combination ofthe two. The communication client(s) 304 stored in the system memory 302may enable user equipment 300 to initiate and carry on communicationsessions. The communication client(s) 304 may include voice callhandlers, video calling clients, gaming and media clients, etc. Thecommunication client(s) 304 may utilize a policy, preferences, etc., indetermining which of a number of available access networks thecommunication client(s) 304 should use in initiating communicationsessions. For example, the communication client(s) 304 may utilize apolicy or preference that prefers LAN access networks to LTE accessnetworks, LTE access networks to GSM access networks, and GSM accessnetworks to other circuit-switched access networks.

The capability module 306 may be configured to determine or reportcapabilities of a communication session. Some capabilities of acommunication session are determined by individual terminals (e.g.,whether or not a terminal is capable of videoconferencing) and some aredetermined by core network devices (e.g., whether multi-partyconferencing can be performed). Accordingly, for example, the capabilitymodule 306 can populate SIP headers or other protocol fields to indicateones of the capabilities of the communication session that aredetermined by user equipment 300. The capability module 306 may alsonegotiate preconditions, quality of service (QoS) parameters, orcapabilities with core network device(s) or with other terminal(s)participating in the communication session.

The SIP client 308 may participate with the communication client(s) 304in initiating a communication session by, for example, formulating SIPREGISTER or INVITE requests and sending the requests to thetelecommunications network. The radio resource control 310 may interactwith the radio 318 and other modules and components of user equipment300 in order to tune the radio 318 and communicate using the radio 318.

In some embodiments, the processor(s) 312 is a central processing unit(CPU), a graphics processing unit (GPU), or both CPU and GPU, or anyother sort of processing unit. Example processing units includeField-programmable Gate Arrays (FPGAs), Application-specific IntegratedCircuits (ASICs), Application-specific Standard Products (ASSPs),System-on-a-chip systems (SOCs), Complex Programmable Logic Devices(CPLDs), Digital Signal Processors (DSPs), and processors incorporatingmore than one type of device (e.g., a CPU and an FPGA on a single die).

User equipment 300 can also include additional data storage devices(removable and/or non-removable) such as, for example, magnetic disks,optical disks, or tape. Such additional storage is illustrated byremovable storage 314 and non-removable storage 316, although any givenuser equipment 300 may have neither of those, or may only have one ofthose. Tangible computer-readable media may include volatile andnonvolatile, removable and non-removable media implemented in any methodor technology for storage of information, such as computer readableinstructions, data structures, program modules, or other data. Systemmemory 302, removable storage 314 and non-removable storage 316 are allexamples of computer-readable storage media. Computer-readable storagemedia include, but are not limited to, RAM, ROM, EEPROM, flash memory orother memory technology, CD-ROM, digital versatile disks (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed byuser equipment 300. Any such tangible computer-readable media may bepart of user equipment 300.

In some embodiments, the radio 318 includes any sort of radio known inthe art. For example, radio 318 may be a radio transceiver that performsthe function of transmitting and receiving radio frequencycommunications. The radio 318 and radio resource control 310 mayfacilitate wireless connectivity between user equipment 300 and variouscell towers, base stations and/or access points of access networks,e.g., packet-switched or circuit-switched networks, whether cellular orLAN-based.

In various embodiments, the display 320 is a liquid crystal display(LCD), organic light-emitting diode (OLED) display, or any other type ofdisplay commonly used in telecommunication devices. For example, display320 may be a touch-sensitive display screen, and can then also act as aninput device or keypad, such as for providing a soft-key keyboard,navigation buttons, or the like.

In some embodiments, the output devices 322 include any sort of outputdevices known in the art, such as a display (already described asdisplay 320), speakers, a vibrating mechanism, or a tactile feedbackmechanism. Output devices 322 also include ports for one or moreperipheral devices, such as headphones, peripheral speakers, or aperipheral display.

In various embodiments, input devices 324 include any sort of inputdevices known in the art. For example, input devices 324 may include acamera, a microphone, a keyboard/keypad, or a touch-sensitive display(such as the touch-sensitive display screen described above). Akeyboard/keypad may be a push button numeric dialing pad (such as on atypical telecommunication device), a multi-key keyboard (such as aconventional QWERTY keyboard), or one or more other types of keys orbuttons, and may also include a joystick-like controller and/ordesignated navigation buttons, or the like.

FIG. 4 illustrates a component level view of an anchoring network device400 capable of implementing call-control functions of a communicationsession of user equipment, and related components. The anchoring networkdevice 400 may represent any sort of user equipment or core networkdevice, such as call-control component(s) 112, MSS 216, MME 208, I-CSCF230, S-CSCF 232, or TAS 234. As illustrated, the anchoring networkdevice 400 comprises a system memory 402 storing aidentifier-determination module 404, mapping data 406, a modificationmodule 408, a session module 410, and a data-update module 412. Thesession module 410 may be configured as a SIP user-agent client (UAC),user-agent server (UAS), proxy, or B2BUA. Also, the anchoring networkdevice 400 includes processor(s) 414 and may include at least one of aremovable storage 416, a non-removable storage 418, transceiver(s) 420,output device(s) 422, or input device(s) 424, any or all of which can becommunicatively connected via bus 426. In some examples, transceiver(s)420 can be components of a communications interface 428. Communicationsinterface 428 can include one or more physical or logical portsconfigured for network communication with other devices such as userequipment 300, FIG. 3, or other anchoring network device(s) 400. In someembodiments, the processor(s) 414 is a central processing unit (CPU), agraphics processing unit (GPU), or both CPU and GPU, or any other sortof processing unit described above with reference to processor 312. Insome embodiments, system memory 402 is volatile (such as RAM),non-volatile (such as ROM, flash memory, etc.), or some combination ofthe two.

The identifier-determination module 404 stored in the system memory 402may perform a number of functions, including determining routingidentifiers for communication sessions, e.g., as described above withreference to FIG. 2. Further details of example functions that may beperformed by identifier-determination module 404 are discussed abovewith reference to FIGS. 1 and 2.

The mapping data 406 may include mappings of access-network types orcommunication-session capabilities to routing identifiers, such asmscAddress values (e.g., Table 1) or location prefixes (e.g., Table 2).For example, the mapping data 406 may include a geographical database orother information permitting mapping of values carried in aP-Access-Network-Information (“PANI”) header to an appropriate routingidentifier. Such values (“PANI information”) can be added to a SIPrequest by the UE or an access-network device, e.g., an eNodeB. In someexamples, the address of the user equipment can include PANIinformation. The mapping data 406 can additionally (wholly or partly) oralternatively be stored in a memory or other computer-readable mediadifferent from memory 402.

The session module 410 may enable user equipment to perform a SIPregistration for a communication session with an IMS or componentsthereof. The session module 410 may additionally or alternativelyintercommunicate with user equipment or other core network devices, suchas S-CSCF 232, FIG. 2, to maintain the state of a communication sessionor respond to user requests during the session.

The session module 410 may additionally or alternatively be configuredto receive, via a communications interface such as transceiver(s) 420, asession-initiation message indicating capabilities of a communicationsession, e.g., as described above. The session module 410 may transmitthe routing identifier and state information of the communicationsession via the communications interface to a call-control server and toreceive, from the call-control server via the communications interface,control information. This can be done, e.g., as discussed above withreference to FIG. 2.

The session module 410 may additionally or alternatively be configuredto receive an indication of user equipment, transmit a request forregistration information corresponding to the user equipment, andreceive the session-initiation message indicating capabilities inresponse to the transmitted request, e.g., as discussed above withreference to FIG. 2.

The modification module 408 can interoperate with the session module 410to permit implementation of call-control functions. For example, controlinformation from the call-control server 236 (e.g., received viacommunications interface 428) can indicate that a party should be addedto, transferred into or out of, or removed from a communication session.Modification module 408 can, in response to that control information,direct session module 410 to transmit a SIP INVITE, REFER, or BYErequest, respectively, to the relevant party.

Modification module 408 or data-update module 412 can be configured toreceive a modification instruction and modify the mapping data 406 inresponse to the modification instruction. For example, modificationmodule 408 or data-update module 412 can transmit requests formodification instructions or responses to modification instructions,e.g., Diameter requests or responses to HSS/HLR 228, to update userinformation corresponding to UE 202 or other mapping information inmapping data 406.

The example anchoring network device 400 also includes additional datastorage devices (removable and/or non-removable) such as, for example,magnetic disks, optical disks, or tape. Such additional storage isillustrated in FIG. 4 by removable storage 416 and non-removable storage418. System memory 402, removable storage 416 and non-removable storage418 are all examples of computer-readable storage media. Tangiblecomputer-readable media and computer-readable storage media can be asdiscussed above with reference to removable storage 314 andnon-removable storage 316.

In some embodiments, the transceivers 420 include any sort oftransceivers known in the art. For example, transceivers 420 may includea radio transceiver that performs the function of transmitting andreceiving radio frequency communications. Also, or instead, thetransceivers 420 may include other wireless or wired connectors, such asEthernet connectors or near-field antennas. The transceivers 420 mayfacilitate connectivity between a public network, such aspacket-switched access network 210, and one or more other devices of atelecommunications network. In some examples, transceivers 420 includeone or more wired transceivers communicatively connected, e.g., via SS7,IP, or IPv6 network links, with S-CSCF 232 or call-control server 236(shown in phantom).

In some embodiments, the output devices 422 include any sort of outputdevices known in the art, e.g., as described above with reference tooutput devices 322. In various embodiments, input devices 424 includeany sort of input devices known in the art, e.g., as described abovewith reference to input devices 324.

Example Call Flows

FIG. 5 is a partial call flow 500 showing examples of call control,e.g., as discussed above with reference to FIGS. 1 and 2. The call flowof FIG. 5 includes UE 502 connected to a telecommunications network viaan access network having a type. UE 502 can be configured to originateor terminate communications sessions. Signaling traffic for acommunication session is proxied by anchoring network device 504, e.g.,TAS 234 or MSS 216.

As shown, anchoring network device 504 receives a session-initiationmessage from MO UE 502, in this example a SIP INVITE. Anchoring networkdevice 504 determines, at 506, that call control may be applicable tothe INVITE, e.g., based at least in part on subscriber information data,such as service key, from HLR/HSS 228. In response to thisdetermination, at 508, anchoring network device 504 determines a routingidentifier, e.g., as described above with reference to FIG. 2. The SIPINVITE can include, e.g., PANI information or other information aboutcapabilities of the communication session determined by MO UE 502, andthe routing identifier can be determined based at least in part on thisinformation. Anchoring network device 504 can determine the routingidentifier, e.g., based at least in part on the access-network type oron capability information included in a header or body (or multipleheaders or bodies) of the SIP INVITE request. In an example, theaccess-network type is carried in a PANI header, as discussed above.

Anchoring network device 504 then sends the routing identifier (“ID”)and state information (“STATE”) of the communication session tocall-control server 510. The state information can include, e.g., anindication that the session is in a pre-alerting phase.

Call-control server 510 then sends control information (“CONTROL”) toanchoring network device 504. In response, at 512, anchoring networkdevice 504 modifies the communication session. This can be done, e.g.,as described above with reference to FIG. 2 or 4. For example, anchoringnetwork device 504 can transmit one or more requests or responses(“R/R”), e.g., in SIP, Diameter, or other protocols, to UE 502 or otheruser equipment or network devices. Anchoring network device 504 cantransmit one or more requests or responses to other core network devicesor terminals, e.g., HSS/HLR 228. In the illustrated example, at leastone of the responses is a SIP 100 Trying response to UE 502, indicatingthat that the communication session is proceeding. In another example,if call-control server 510 indicates the communication session shouldnot proceed, e.g., because the user's prepaid-minutes balance is zero,anchoring network device 504 can transmit a SIP 402 Payment Requiredresponse or a SIP 488 Not Acceptable Here response.

FIG. 6 is a partial call flow 600 showing examples of call control.Anchoring network device 602 proxies a SIP INVITE from an originatingparty to MT UE 604. In some examples, the SIP INVITE can be asession-initiation message. In the illustrated example, MT UE 604responds to the INVITE with a SIP 183 Session in Progress response, andthe SIP 183 response is the session-initiation message. The SIP 183response can include, e.g., including information used for negotiatingpreconditions or QoS of the communication session, PANI information, orother information about capabilities of the communication sessiondetermined by MT UE 604.

At 606, anchoring network device 602 determines whether call control isneeded, e.g., based on service keys or other information. If so, at 608,anchoring network device 602 determines a routing identifier (“ID”),e.g., as described above. Anchoring network device 602 transmits therouting identifier and state information of the communication session(“STATE”) to call-control server 610, which responds with controlinformation (“CONTROL”). In response, at 612, anchoring network device602 modifies the communication session, e.g., by transmitting one ormore SIP requests or responses. In the illustrated example, at least oneof the responses is a SIP 183 response towards the MO UE to continuesetup of the communication session.

Example Processes

FIGS. 7 and 8 illustrate example processes. These processes areillustrated as logical flow graphs, each operation of which representsone or more operations that can be implemented in hardware, software, ora combination thereof. In the context of software, the operationsrepresent computer-executable instructions stored on one or morecomputer-readable storage media that, when executed by one or moreprocessors, perform the recited operations. Generally,computer-executable instructions include routines, programs, objects,components, data structures, and the like that perform particularfunctions or implement particular abstract data types. The order inwhich the operations are described is not intended to be construed as alimitation, and any number of the described operations can be combinedin any order and/or in parallel to implement the processes. Similarly,the order of data exchanges shown in example call flows of FIGS. 7 and 9is not intended to be construed as a limitation.

FIG. 7 illustrates an example process 700, e.g., a computer-implementedmethod, performed by an anchoring network device of a telecommunicationsnetwork (e.g., TAS 234) for enabling call control of a communicationsession. The anchoring network device can, e.g., include a serviceswitching function (SSF) such as a CAMEL SSF or gsmSSF. In someexamples, a system includes a computer-readable memory and of ananchoring network device configured to perform respective functionsdiscussed below with reference to FIG. 7.

The process includes, at 702, receiving, by the anchoring networkdevice, an indication of an access-network type (or identifier, or othercapability information, and likewise throughout) of a communicationsession of user equipment. The indication can include, e.g., PANIinformation carried in a SIP header.

At 704, the anchoring network device determines a routing identifierbased at least in part on the indication of the access-network type.This can be done, e.g., as discussed above with reference to FIG. 2. Insome examples, the routing identifier includes at least an address or alocation prefix.

At 706, the anchoring network device transmits an indication of a stateof the communication session to a call-control server, e.g., of thetelecommunications network or communicatively connected therewith, inassociation with the routing identifier. The indication can includeinformation that a particular state is ongoing, e.g., that a call is inprogress, or that a state has change, e.g., that a call has just goneoff- or on-hook, or that DTMF digits have been detected in audio data ofthe communication session. Other examples are described above.

FIG. 8 illustrates an example process 800, e.g., a computer-implementedmethod, performed by an anchoring network device of a telecommunicationsnetwork (e.g., TAS 234) for carrying out call control of a communicationsession. Blocks 702, 704, and 706 can be as described above withreference to FIG. 7. Block 706 can be followed by block 802.

The process includes, at 802, receiving, by the anchoring networkdevice, a response from the call-control server. The response caninclude, e.g., control information of the communication session asdescribed above with reference to FIG. 2, 5, or 6,

At 804, the anchoring network device modifies the state of thecommunication session based at least in part on the response. This canbe done, e.g., as described above with reference to FIG. 2. In someexamples, at 804, the anchoring network device can add a participant tothe communication session, e.g., by transmitting a SIP INVITE; remove aparticipant from the communication session, e.g., by transmitting a SIPBYE request or a SIP 4xx, 5xx, or 6xx response; transferring thecommunication session, e.g., by sending a SIP REFER request; updatingcharging records of the communication session (e.g., to indicate aspecific per-minute rate); updating consumption counters of thecommunication session (e.g., prepaid minutes used); updating consumptionlimits of the communication session (e.g., prepaid minutes remaining);or other modifications described above.

Associating connection-state information with a routing identifier asdescribed above permits adjusting call control based on characteristicsof each individual communication session. This can provide improvedperformance and reduce waste of network bandwidth compared withattempting to provide advanced call-control services for a particularterminal without reference to its connection environment. Customizingcall control based on the communication session may also permit applyingonly those call-control services relevant to a particular communicationsession, reducing user frustration. Using a routing identifier can alsoprovide improved isolation between the anchoring network devices and thecall-control servers. Using a routing identifier can also provide thecall-control servers with information about the connection withoutrequiring that the call-control servers be programmed to operate withthe full SIP protocol.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as example forms ofimplementing the claims.

What is claimed is:
 1. A telecommunications network, comprising: acall-control server; and an anchoring network device configured to:proxy signaling traffic for a communication session; determine a routingidentifier based at least in part on information of the one of a firstaccess network of a first type and a second access network of a second,different type carrying the communication session; and transmit stateinformation of the communication session to the call-control server inassociation with the routing identifier.
 2. The telecommunicationsnetwork of claim 1, wherein the call-control server is responsive to thestate information of the communication session to transmit controlinformation of the communication session to the anchoring networkdevice.
 3. The telecommunications network of claim 2, wherein theanchoring network device is configured to add or drop one or moreparties to the communication session in response to the controlinformation.
 4. The telecommunications network of claim 2, wherein: thecall-control server is configured to transmit the routing identifier inassociation with the control information; and the telecommunicationsnetwork further comprises a routing network device configured to:determine a network address of the anchoring network device based atleast in part on the routing identifier transmitted in association withthe control information; and convey the control information to theanchoring network device using the determined network address.
 5. Thetelecommunications network of claim 1, wherein the call-control serverincludes a Customised Applications for Mobile network Enhanced Logic(CAMEL) server.
 6. The telecommunications network of claim 1, whereinthe anchoring network device includes a telephony application server(TAS).
 7. The telecommunications network of claim 1, wherein theanchoring network device is configured to determine an access-networktype of the communication session based at least in part on thesignaling traffic and to determine the routing identifier using a storedmapping of access-network types to corresponding routing identifiers. 8.The telecommunications network of claim 1, wherein the first type is apacket-switched cellular type and the second type is a packet-switchedlocal-area-network type.
 9. A computer-implemented method comprising:receiving, by an anchoring network device of a telecommunicationsnetwork, an indication of an access-network type of a communicationsession of user equipment; determining, by the anchoring network device,a routing identifier based at least in part on the indication of theaccess-network type; and transmitting, by the anchoring network device,an indication of a state of the communication session to a call-controlserver in association with the routing identifier.
 10. Thecomputer-implemented method of claim 9, further comprising: receiving,by the anchoring network device, a response from the call-controlserver; and modifying, by the anchoring network device, the state of thecommunication session based at least in part on the response.
 11. Thecomputer-implemented method of claim 10, wherein the modifying comprisesat least adding a participant to the communication session, removing aparticipant from the communication session, transferring thecommunication session, updating charging records of the communicationsession, updating consumption counters of the communication session, orupdating consumption limits of the communication session.
 12. Thecomputer-implemented method of claim 9, wherein the anchoring networkdevice includes a service switching function (SSF).
 13. Thecomputer-implemented method of claim 9, wherein the routing identifierincludes at least an address or a location prefix.
 14. An anchoringnetwork device comprising: a communications interface; one or morecomputer-readable media having thereon a plurality of modules; and aprocessing unit operably coupled to at least one of thecomputer-readable media and to the network interface, the processingunit adapted to execute modules of the plurality of modules comprising:a session module configured to receive, via the communicationsinterface, a session-initiation message indicating capabilities of acommunication session; an identifier-determination module configured todetermine a routing identifier of the anchoring network device based atleast in part on the capabilities; and a modification module; whereinthe session module is further configured to transmit the routingidentifier and state information of the communication session via thecommunications interface to a call-control server and to receive, fromthe call-control server via the communications interface, controlinformation; and the modification module is configured to modify thecommunication session based at least in part on the control information.15. The anchoring network device of claim 14, wherein the capabilitiesinclude at least an identifier of an access network of the communicationsession, an access-network type of the communication session, a devicetype of user equipment participating in the communication session,location information of the user equipment, a media capability of theuser equipment, a virtual-network identifier of the user equipment, oran authentication type of the user equipment.
 16. The anchoring networkdevice according to claim 14, wherein the anchoring network deviceincludes at least a mobile switching center (MSC), an MSC server (MSS),a TAS, an SSF, a GSM SSF (gsmSSF), or an Internet Protocol (IP)Multimedia Subsystem SSF (IM-SSF).
 17. The anchoring network deviceaccording to claim 14, wherein the session-initiation message includes aSession Initiation Protocol (SIP) INVITE request or a SIP 183 responseand the capabilities of the communication session are indicated in atleast one SIP header in the session-initiation message.
 18. Theanchoring network device according to claim 14, wherein the sessionmodule is further configured to: receive an indication of userequipment; transmit a request for registration information correspondingto the user equipment; and receive the session-initiation messageindicating capabilities in response to the transmitted request.
 19. Theanchoring network device according to claim 14, further comprising adata-update module of the plurality of modules and a memory storing amapping between capabilities and routing identifiers, the data-updatemodule configured to receive a modification instruction and modify themapping in response to the modification instruction.
 20. The anchoringnetwork device according to claim 14, the identifier-determinationmodule further configured to determine the routing identifier includinga location prefix and transmit, in association with the routingidentifier, an address of user equipment participating in thecommunication session.